Blog | 66 - Glorious Gamma
| Freelance Photographer in St Ives Cambridgeshire: Food & Drink Photography; Commercial Photography, Product Photography & Packshot Photography; Event Photography; Portrait Photography; Corporate Photography & PR Photography; Engagement Photography & Wedding Photography and Photography Training Courses in Cambridge, Huntingdon, Peterborough, Bedford, Ely, St Neots, St Ives and London. Professional Photography Services in St Ives, St Neots, Huntingdon, Bedford, Peterborough, Ely & Cambridge. | |||
 
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Alistair Grant Freelance Photographer Cambridge & London |
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bokeh photographic: Blog No: 66 → TIP: Click any image to view in LightBox |
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Glorious Gamma In addition to what camera buttons do what (which is what most photography training courses seem to limit themselves to and furthermore they do this without explanation!) all bokeh photographic Photography Training emphasises getting to know your own camera’s performance in real life scenarios. The starting point is teaching participants to think (or should that be see?) like a photographer. Whilst a full explanation is beyond the scope of this blog post here’s a (very) simplified explanation that will hopefully pique your interest in enrolling. A digital sensor responds to light in a linear manner. That is, when light intensity is doubled the picture elements (aka ‘pixels’) record the doubling of the number of photons hitting the light-sensitive element and output is thus doubled i.e. the digital signal is in direct proportion to the light intensity. Along with analogue film our eyesight differs because, along with most human physiological senses, it is highly non-linear. If light intensity is doubled we perceive the light to be brighter but not twice as bright. Such compression is functionally important as it allows us to simultaneously perceive shadow detail alongside highlight detail. In addition, it allows us to see across an extremely wide range of light i.e. from a dark interior to bright outdoors. Moreover, our eyesight is relatively more sensitive to changes in dark tones than changes in light tones; an evolutionary artefact from the time before artificial lighting. Photography involves a lot of trade-offs and one of the most important is achieving a graduation in tones acceptable to our eyesight whilst minimising digital noise in the shadows. This concept is perhaps easier to explain using the specifications of a real camera so let’s take Canon’s new entry-level EOS 2000D. Most people fall into the trap of fixating only upon megapixels which in the 2000D’s case is 24.1 MP i.e. the camera can produce a 6000 pixel x 4000 pixel image = 24,000,000 pixels. However, this is more a measure of maximum physical print size and not necessarily quality in terms of information capture. In any given digital sensor each individual pixel is represented by a given number of bits where a greater number of bits equates to higher image quality as more information can be recorded. For example, in terms of black and white: an 8 bit pixel can record pure black (0), pure white (255) or any of the 254 intermediate tones in-between; a 10 bit pixel can record pure black (0), pure white (1,024) or any of the 1,022 intermediate tones in-between; a 12 bit pixel can record pure black (0), pure white (4,096) or any of the 4,094 intermediate tones in-between; and a 14 bit pixel (Canon’s EOS 2000D) can record pure black (0), pure white (16,384) or any of the 16,382 intermediate tones in-between. The number of bits contributing to each pixel is usually expressed as bit depth per red, green and blue channel i.e. an 8 bit pixel has three channels of 8 bits making a total bit depth of 24. One of the consequences of linear response is that half (8,192) of the 16,384 tones captured by the Canon 2000D’s digital sensor are allocated to the brightest stop of light in a scene, half of the remainder (4,096) are allocated to the next brightest stop of light, half of the remainder (2,048) are allocated to the next brightest stop of light and so on. The net effect is rather than a smooth continuous graduation the tonal distribution is perceptually non-uniform being weighted towards the highlights (which our eyes are relatively insensitive to) with much fewer tones making up the shadows which our eyesight is more sensitive to. A non-encoded image appears dark and lacks contrast until gamma encoding is applied during RAW conversion which normalises the histogram – see Image Key. Note that even when shooting RAW the preview image on a camera's LCD screen is a gamma-encoded JPEG. Working at a higher bit depth will not necessarily affect highlight capture but it generally improves shadow capture, especially for over-scaled (high-contrast) scenes, within the dynamic range of the camera. However, balancing acceptable graduation in tones versus digital noise in the shadows is challenging for even experienced photographers. ‘Exposing for the highlights whilst developing for the shadows’ sounds straightforward but pushing to just below the threshold of overexposure is difficult to judge, especially when in-camera gamma correction can give false-positive highlight clipping, whilst different cameras differ in noise performance and therefore the points at which inherent noise outweighs the benefits of boosting the shadows in post-production. Returning to where I began the starting point in getting participants to think/see like a photographer is helping them recognise tonal graduation in scenes which, although trickier than it might sound, is the absolute foundation to good photography. Browse the Photography Services I offer to see what I mean.
Image Key: Left hand side of image represents a linear gradient (gamma = 1) where although the highlights are reasonably preserved there is compression of the midtones and significant blocking of the shadows. The tonal distribution is perceptually non-uniform being weighted towards the highlights with much fewer tones making up the shadows. Right hand side of image represents a gamma-encoded gradient (gamma = 2.2) where the histogram has been normalised and tonal distribution is smooth and perceptually uniform |
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Call Alistair Grant on 07775 365507, Email [email protected] or click Booking Enquiries if you have any questions or would like to make a booking. |
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bokeh: "the aesthetic quality of the blur produced in the out-of-focus parts of an image produced by a lens" Freelance Photographer offering Food & Drink Photography Cambridge; Commercial Photography Cambridge, Product Photography Cambridge & Packshot Photography Cambridge; Event Photography Cambridge; Portrait Photography Cambridge; Corporate Photography Cambridge & PR Photography Cambridge; Engagement Photography Cambridge & Wedding Photography Cambridge and Photography Training Courses in Cambridge. Also covering: Huntingdon, St. Ives, Ramsey, St. Neots, Peterborough, Bedford, Stamford, Newmarket, Sawtry, Alconbury Weston, Brampton, Hartford, Warboys, Houghton, Wyton, Godmanchester, Hilton, Hemingford Grey, Hemingford Abbots, Fenstanton, Whittesley, Yaxley, Needingworth, Somersham, Chatteris, Ely, Bar Hill, Grafham and Buckden. |
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bokeh photographic - Alistair Grant | Freelance Photographer | Cambridge, London, UK - Creative Natural Photography And Outstanding Customer Service At Competitive Prices - Food & Drink Photography | Commercial Photography & Product Photography | Corporate Photography & PR Photography | Portrait Photography (inc. 'Active Portraiture', 'Naturally You' & 'Poptraits') | Event Photography | Engagement & Wedding Photography | Photography Training Courses & Camera Tuition | Videography & Film Production Tel: 07775 365507 | Email: [email protected] |
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